The present invention relates to a sensor comprising a sensing element and an evaluation unit, in which the output signals from the sensing element are weighted with at least one switching threshold for generating object detection signals.
Sensors of this type are generally used for detecting objects and can be embodied as optical sensors, ultrasonic sensors and the like.
A sensor of this type is normally provided with a sensing element for detecting objects. The sensor is furthermore provided with an evaluation unit for evaluating the output signals from the sensing element. In the process, the output signals are weighted with the aid of one or several switching thresholds, thereby generating an object detection signal, which indicates whether or not an object has been detected, preferably within a specified area.
An optical sensor in the form of a light sensor, such as a photoelectric sensor, is one example for such a sensor. This light sensor is provided with a sensing element that consists of a transmitter for emitting light rays and a receiver for receiving light rays, which are connected to the evaluation unit and are integrated into a joint housing together with the evaluation unit.
For detecting an object, the light rays emitted by the transmitter are conducted to the object. These light rays are reflected by the object and then travel back as receiving light rays to the receiver. The output signals from the sensing element are the receiving signals of the receiver. These signals are weighted with a switching threshold for generating a binary object detection signal. The switching threshold defines a detection distance which, in turn, defines an area of coverage. Depending on whether the currently received signal is located above or below the switching threshold, the object detection signal assumes either the switching state “object detected in the detection range” or “detection range clear.”
The switching threshold for light sensors of this type is determined during a teach-in process. Following the triggering of such a teach-in process, e.g. by activating a button on the sensor, an object is placed relative to the sensor at the detection distance to be set for the sensor. Following this, the object arranged at the detection distance is scanned with the aid of transmitted light rays and is thus detected. The switching threshold value is then derived from the receiving signals at the receiver output, which are recorded in the process. In the simplest case, the level recorded for the receiving signals is adopted directly as a switching threshold. Besides the value for the receiving signal level, an additional value that is stored in the evaluation unit, a so-called functional reserve, is preferably also added and the sum formed in this way is adopted as the switching threshold. The teach-in process is thus completed and the sensor operation can start, wherein during the operating phase for generating the object detection signal, the currently recorded receiving signals are compared to the switching threshold. If the switching threshold must be changed, then a new teach-in process must be realized, which requires a considerable expenditure in time.